1. Field of the Invention
This invention relates to traffic noise barriers. More specifically, this invention relates to a crashworthy traffic noise barrier system for bridge rails and other longitudinal barriers.
2. Description of the Related Art
Traffic noise barrier walls serve to shield otherwise quiet areas from noise caused by automotive, railway, aircraft, marine, or pedestrian traffic. A typical traffic noise barrier wall is from about 4 to 24 feet in height and runs continuously alongside a selected section of a roadway, railway, aircraft runway, waterway, parking lot, walkway, and the like.
One common design of a traffic noise barrier wall includes a plurality of panels of wood or concrete supported by vertically mounted posts. Examples of such noise barrier walls are found in U.S. Pat. Nos. 5,713,170 and 5,537,788, both issued to Elmore et al. Noise barrier walls of this type are suitably sturdy and effective in reducing highway noise; however, such noise barrier walls are usually not designed for vehicle impact. As a result, these noise barriers are located many feet (e.g., 40 feet) from the normal path of traffic. Problematically, space constraints often require that noise barriers be located closer to the path of traffic. One example is when a noise barrier is required on a bridge.
Where space constraints exist, it is not uncommon for noise barriers to be mounted on top of a crashworthy traffic barrier. One example of such an arrangement is found in U.S. Pat. No. 4,214,411 issued to Pickett, wherein panels of transparent material are secured between beams mounted on top of a roadside barrier. The transparent panels are effective in providing travelers on the traffic path with a view outside the roadway. However, vehicles impacting the otherwise crashworthy traffic barrier may also strike the noise barrier, creating potential hazards to the impacting vehicle and nearby pedestrians.
The U.S. Federal Highway Administration (FHWA) requires all longitudinal barriers used on the National Highway System (NHS) to be crashworthy and to qualify as such according to the testing and acceptance guidelines of the National Cooperative Highway Research Program (NCHRP) Report No. 350, which is incorporated by reference herein in its entirety. Under NCHRP Report No. 350, longitudinal barriers include any device whose primary functions are to prevent vehicular penetration and to safely redirect an errant vehicle away from a hazard outside the normal path of the vehicle (e.g., outside the roadway). Longitudinal barriers include, for example, roadside barriers, median barriers, and bridge rails. For longitudinal barriers, NCHRP Report No. 350 defines six test levels, each of which prescribe test conditions appropriate for a range of highway types, traffic volumes, and other parameters. Test Level 1 (TL-1) and Test Level 2 (TL-2) are intended for low-speed and/or low-volume roads, while Test Level 3 (TL-3) through Test Level 6 (TL-6) are intended for high-speed facilities with increasingly higher traffic volumes. TL-1, TL-2, and TL-3 require redirection of an 820-kg car impacting a barrier at 20 degrees, and a 2,000-kg pickup truck impacting a barrier at 25 degrees, at speeds of 50 km/h, 70 km/h, and 100 km/h, respectively. TL-4 adds an 8,000-kg single-unit truck at 15 degrees and 80 km/h to the TL-3 matrix; TL-5 substitutes a 36,000-kg tractor/van trailer for the single-unit truck. TL-6 substitutes a 36,000-kg tractor/tank trailer. Thus, to be used on the NHS, a longitudinal barrier must be accepted by the FHWA as meeting one or more test levels of NCHRP 350. Such acceptance is typically indicated in a letter from the FHWA to the manufacturer of the longitudinal barrier or in a published memo from the FHWA.
Although NCHRP Report No. 350 offers guidance for the safety performance evaluation of longitudinal and other traffic barriers, it offers no guidance toward the evaluation of attachments on or near these barriers. Some guidance toward the evaluation of barrier attachments to barriers is provided in a technical paper entitled “Guidelines for Attachments to Bridge Rails and Median Barriers” by Keller et al. Using the Test Levels outlined in NCHRP Report No. 350, Keller et al. identify a “Zone of Intrusion” (ZOI) for a wide variety of traffic barriers, including sloped-face concrete parapets (e.g., New Jersey, Single Slope, F-shape, and open concrete rail), vertical-faced concrete parapets (e.g., vertical wall and open concrete rail), steel corrugated rails (e.g., W-beam and thrie beam), steel tubular rails, steel tubular rails on curbs, combination concrete and steel tube railings, and timber bridge rails. The ZOI represents an envelope around the barrier into which various vehicular components intrude upon the vehicle's impact with the barrier.
For noise barriers and similar attachments, referred to by Keller et al. as “continuous attachments”, Keller et al. provide various design considerations that allow such attachments to be placed in the ZOI. One suggestion is to use attachments that will breakaway, allowing the system to deflect upon impact by a vehicle. Where non-breakaway attachments are used, Keller et al. suggest that the design take into account the snag potential of the attachment. Snagging is when a portion of a vehicle engages a vertical element, such as a post, causing deceleration of the vehicle. In addition to snagging concerns, Keller et al. suggest that the potential implications of debris from impacts on these systems be considered because debris associated with the attachment may fall on traffic and/or pedestrians around or below the barrier. Keller et al. also suggest that vehicle occupant compartment intrusion and deformation be considered. Occupant compartment intrusion and deformation is a concern for traffic barrier attachments under two scenarios: (1) a vehicle component is driven into the occupant compartment due to impact with the attachment; or (2) the attachment itself intrudes into or deforms the occupant compartment. While Keller et al. provide various guidelines for the design of barrier attachments, Keller et al. fail to provide a design for a traffic noise barrier wall that would meet their guidelines.
Thus, there is a need for a traffic noise barrier wall for use where space constraints require the noise barrier wall to be located near a selected section of a roadway, railway, aircraft runway, waterway, parking lot, walkway, and the like, and which will prevent vehicle deceleration due to snagging, will reduce or eliminate occupant compartment intrusion and deformation, and which will reduce or eliminate falling debris concerns.